Post on 07-Dec-2021
Environmental pollution produced by gold artisanal mining in the Mapiririver basin, Apolobamba, Bolivia
K.S. Villegas , P. Alfonso , P. Higueras , S. Palacios , J.M. Esbrí , E.M. García-Noguero(1) (2) (3) (2) (3) (3)
(1) Escuela de Postgrado, Universidad Técnica de Oruro, Oruro, Bolivia.,
(2) Dept. Enginyeria Minera i Recursos Naturls, Universitat Politècnica de Catalunya, Manresa, Spain
(3) Instituto de Geología Aplicada, Universidad de Castilla-La Mancha, Almadén, Spain
IntroductionMining activity is very important in Bolivia since colonial times. Nowdays
it has been reactivated, especially gold mining, due to rise in metal prices.
Artisanal and small-scale mining activities are abundant in the protected
area of Apolobamba, department of La Paz; it is located near the border with
Peru. Several rivers occur in this area, The most important are the river
Suches, in the border with Peru, that drain to the Titicaca Lake and the
Mapiri river, that is afluent to theAmazonas river.
In the northern part of this area gold is mined from veins. Here mercury is
used to recovery gold by obtaining an Hg-Au amalgam. This manipulation
with mercury causes an important environmental impact in the area.
otherwise, i
The present work is a preliminary study of the contamination of the Mapiri
river basin in the Apolobamba area, which drain into the Amazonas river.
The present study also aims to do a preliminary evaluation of the efectivity
in gold recovery of the amalgamation method in this area.
In the head of this basin, located at more than 4000 m above sea level.
According to Hentschel et al (1999) about 15 tones of Hg are discharged in
the environment in Bolivia every year.
Another additional problem to the use of mercury to gold recovery is the
price that is increasing a very high rates due to the low production of
mercury due to the European Comunity phobitition to produce it for its
members.
n the south part of the Mapiri basin gold is in placer-type
deposits and it is obtained by mechanical techniques without the use of
mercury.
Geology
Sampling
In the Apolobamba protected area gold occurs as primary
and secondary deposits. In the northern part of the Mapiri
river basin gold occurs in hydrothermal quartz veins of
Paleozoic age. The area is abundantly covered by
quaternary sediments. In other cases as in theSuches river
and in the southern part of the Mapiri river basin, gold
occurs in placer-type deposits, where it is free, but it occurs
in very small particles.
Veins, that constitute the primary gold deposits, are hosted
in metasedimentary rocks, mainly shales and schists. Quartz
veins often also contain sulphides as pyrite, sphalerite,
galena,arsenopyrite, chalcopyrite and sulphosalts and
telurides.
We have sampled several mining sites from this area, in
particular the ones known as Viscachani, Virgen del
Rosario, Flor de Mayo and Chojlaya, located in the
proximity of the head area of the Mapiri river and the head
of the Tuichi river. Also the exploitations in the proximity of
the locality of Mapiri, in the south of the aplolobamba were
sampled.
All these mining sites were in activity during the present
sampling campaign.The processing of gold takes place near
the mines, where the mines also live.
Discussion and ConclusionsThe artisanal gold mining activities in the northern part
of the Mapiri river basin use mercury to the gold
recovery processment. They led to an intense
environmental pollution, mainly related to mercury and
arsenic contents. Mercury pollution is due to the use of
this element to do an amalgame with gold as a recovery
tecnique.
Tailings from Chojlaya also are rich in heavy metals as
Pb, Cu, Cd and Se. These contents produce
contamination of soils and water.
Vegetation of the area is very effective in capturing Hg,
then it could be used as a fitoremediation system to
reduce the contamination of mercury in the water
courses of the area. In addition, in the surroundings of
Viscachani large deposits of bentonite occur. These
clays could also be used to reduce the Hg and As
pollution in water by making barriers .
As content is important in several mine sites. Arsenic
come from the destruction of arsenapyrite, wich is
present as an abundant mineral in many locations of
mining activity. In addition to the envirommental
contamination caused by this component, the content of
As makes difficult the amalgamation of gold and
mercury; in these cases more mercury is necessary to
added to obtain the amalgamation and gold recovery.
Then, in these cases the use of mercury is specially non
effective in gold recovering.
After processing, tailings still contain important
amounts of gold suggesting that the amalgamation
method is not effective to gold recovering. In some
places silver sulphosalts are abundant, then Ag could be
in ecomomic contents. The Ag content should be
investigated and took into account when exploitation.
More research should be done to quantify other possible
metals that could be of economic interest, as silver. In
addition, an alternative method to the use of mercury
should investigated to be used torecovery gold in these
exploitations, according to the sustanability concept.
AcknowledgementsThis research was financed by the projectAECID:A3/042750/11 and the Consolidated Group for Research of
Mineral Resources, 2009SGR-00444.
Typical vegetation of the area which absorbs
important contents of Hg.
View of the bentonite deposits from
Viscachany.
Analytical methods
The content of several metals were measured by means of XRF
(Se, As, Cu, Zn, Cd, Pb, Hg) in tailing samples from the different
gold mining sites in theACTLABS laboratory.
In addition mercury concentrations in water and in vegetation
close to the processing areas determin by means of atomic
absorption spectrometry with Zeeman effect (LUMEX RA-915
Equipment) in the Universidad castilla-La Mancha.
The concentration of mercury also was determined in the air
along the study area with a portable .
were ed
LUMEX RA-915 Equipment
Maps of the protected area of Apolobamba with the location of the studied artisanal mining activities.
ResultsTailings are mainly constituted by quartz with minor
contents of clay minerals and sulphides. Gold content,
after recovery with mercury, is high, between 4.56
ppm and 10.35 ppm (Table 1).
The Hg content of the tailings ranges from 149 to
1027 ppm. Here, lixiviable mercury ranges between
30.10 and 859.94 ng/l. Water released from the
tailings contains between 0.1 and 5.7 ppb of Hg.
The analysed vegetation, which is typical of the area,
has high Hg contents, from 162 to 219 ppm.
The measurement of the Hg content in the air is
negligible except close the mining activities, where it
can reach up to high values (eg. 4.4 ppm in
Viscachani).
In addition there is a high arsenic content in all the
studied tailings, except in those from the Viscachani
mining site, where concentrations of this element
ranges from 456 ppm to 18540 ppm. The Pb content
usually ranges from 337 to 939 ppm. The Chojlaya
mining site tailing has exceptionally high values of
heavy metals: Pb content is between 2.26 and 3.27
wt.%, Cd ranges from 160 to 228 ppm, Zn from 194 to
794 ppm, Cu from 847 to 1052 ppm and Se from 105
to 187 ppm (Table 2). These contents also contribute
to an environmental pollution.
Extraction of gold by amalgamation with mercury
. Mercury is mixed with the mineral
in ball mills where it is pulverized and gold forms
an amalgam with mercury.
at Viscachani
After the extraction of gold by amalgamation with
mercury, tailings still are rich in gold. Many women of
the area work to recover gold from them.Extraction of gold by amalgamation with
mercury at Flor de Mayo.
View of the large tailings of the Flor de
Mayomining activity.
References
Table 1. Content in Au, Hg and As of tailings from the
Apolobamba potected area.
Table 2. Content (ppm) in different metals of tailings and veins from the Apolobamba
potected area.
La Paz
APOLOBAMBA
ParaguayChile
Peru
N
Brazil
Argentina
Mapiri river
Ulla Ulla
Hilo -Hilo
Suchesriver
Charazani
Virgen del Rosario
Flor de Mayo
Viscachani
0 10 20 km
Mining areas
Sampled localities
0
500
1000
1500
2000
2500
3000
3500
4000
4500
10:48 11:16 11:45 12:14 12:43 13:12 13:40 14:09
Hg
(pp
b)
Time (hour:minute)
Ulla-ulla Viscachani
Graphic of the measurement in situ with the LUMEX portatil spectrometer, of the Hg content in
the air along the road from Ulla Ulla to Viscachani.
Sample Au
ppm
Hg
ppm
As
ppm
M1 Tailing head Tuichi 1.75 75 1790
M2 Tailing head Mapiri 8.40 122 20
M3 Tailing head Mapiri 9.88 364 13462
M5 Tailing lower Mapiri 0.02 2 28
M6 Tailing lower Mapiri 4.56 - -
M7 Tailing lower Mapiri 7.50 - -
M8 Tailing lower Mapiri 10.35 - -
M10 Tailing lower Mapiri 0.04 - -
Location
Hentschel, T., Roque, D., Taucer, E. 1999. Small-scale Gold Mining at San Simon, Bolivia. In:
Small-scale Gold Mining: Examples From Bolivia, Philippines Industrial Activities
Branch, International Labour Office, Geneva. & Zimbabwe, Jennings, N., (Ed.), Working
Paper.
Sample Location Type Cr Ni Cu Zn As Se Mo Cd Hg Pb
P 3 Viscachani Tailing 0 0 17 50 22 21 18 5 210 302
Q 1' Flor de Mayo Tailing 87 23 36 475 18540 0 17 39 255 939
Q 4 Flor de Mayo Tailing 28 0 2 99 4388 0 16 19 149 337
R 4 Chojlaya Tailing 192 45 1052 194 456 187 8 228 232 32704
R 5 Chojlaya Tailing 103 30 847 794 1000 105 26 160 1027 22627
R 12 Chojlaya Vein gouge 537 38 5001 498 613 163 34 207 4 29999
R 6-3 Chojlaya Vein gouge 318 0 0 38 0 49 28 0 0 4138
R 13 Chojlaya Vein 231 10 11 100 7 28 35 39 0 234
R 14 Chojlaya Vein 258 21 35 141 16 25 34 48 0 396
R 6.1 Chojlaya Selected mineral 2120 636 684 781 19298 757 59 6387 388 291837